Messages in this thread Patch in this message | | | From | Jarkko Sakkinen <> | Subject | [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl_release(). | Date | Tue, 15 Dec 2020 23:40:28 +0200 |
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Add synchronize_srcu_expedited() to sgx_encl_release() to catch a grace period initiated by sgx_mmu_notifier_release().
A trivial example of a failing sequence with tasks A and B:
1. A: -> sgx_release() 2. B: -> sgx_mmu_notifier_release() 3. B: -> list_del_rcu() 3. A: -> sgx_encl_release() 4. A: -> cleanup_srcu_struct()
The loop in sgx_release() observes an empty list because B has removed its entry in the middle, and calls cleanup_srcu_struct() before B has a chance to calls synchronize_srcu().
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer") Suggested-by: Haitao Huang <haitao.huang@linux.intel.com> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org> --- arch/x86/kernel/cpu/sgx/encl.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index ee50a5010277..fe7256db6e73 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -438,6 +438,12 @@ void sgx_encl_release(struct kref *ref) if (encl->backing) fput(encl->backing); + /* + * Each sgx_mmu_notifier_release() starts a grace period. Therefore, an + * additional sync is required here. + */ + synchronize_srcu_expedited(&encl->srcu); + cleanup_srcu_struct(&encl->srcu); WARN_ON_ONCE(!list_empty(&encl->mm_list)); -- 2.27.0
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